Document AnnotationsTransformer (#5247)

* Restructure existing Reference docs

Restructure Reference section for site to better match k8s.io. Change
descriptions to complete sentences. Improve instructions to locally load
site.

* Document AnnotationsTransformer on site

Dcoument AnnotationsTransformer API under Reference on site.

* Document required fields

Document required fields and explain effects of optional ones.

* Make site setup instructions more explicit

* Link required K8s fields

site/content/en/docs/Reference/API/Common Definitions/FieldSpec.md

@@ -0,0 +1,32 @@
+---
+title: "FieldSpec"
+linkTitle: "FieldSpec"
+weight: 1
+date: 2023-07-28
+description: >
+  FieldSpec specifies a field for Kustomize to target.
+---
+
+* **group** (string)
+
+  Kubernetes group that this FieldSpec applies to.
+  If empty, this FieldSpec applies to all groups.
+  Currently, there is no way to specify only the core group, which is also represented by the empty string.
+
+* **version** (string)
+
+  Kubernetes version that this FieldSpec applies to.
+  If empty, this FieldSpec applies to all versions.
+
+* **kind** (string)
+
+  Kubernetes kind that this FieldSpec applies to.
+  If empty, this FieldSpec applies to all kinds.
+
+* **path** (string)
+
+  Path to target field. Fields in path are delimited by forward slashes "/".
+
+* **create** (bool)
+
+  If true, creates fields in **path** not already present.